The propagation of microbial cells to obtain fermentation products, including propionic acid, is well known. Recently, there has been considerable interest in fermentation processes which can be used to produce chemicals from carbohydrate feed stocks instead of petroleum feed stocks.
In U.S. Pat. No. 4,425,432, a microbial method is disclosed for preparing acetic and butyric acid as fermentation products from carbohydrates. It also is known that Propionibacterium will produce propionate, acetate and carbon dioxide as the major end products of carbohydrate fermentation. For example, Propionispira arboris ferments 1.5 moles of glucose into propionate, acetate and carbon dioxide in a 2:1:1 ratio and ferments 3 moles of fumarate into propionate, acetate and carbon dioxide in a 2:1:4 ratio. Since propionic acid or propionate is a more valuable chemical than acetate or carbon dioxide, it obviously would be desirable to develop a microbial process in which propionic acid or propionate production is increased at the expense of acetate and carbon dioxide formation.